Known LED-based light sources have been implemented to provide either colorful decorative lighting or a constant white light illumination. In a decorative application, such sources may include several LEDs providing light output in different colors, for example, red, green, or blue, depending on the material composition of the LED. It is also known to construct an assembly that produces a color different from the output color of the LED, by converting the LED light output having a peak wavelength (the “primary light”) to light having a different peak wavelength (the “secondary light”) using luminescence/fluorescence.
The luminescent/fluorescence process involves absorbing the primary light by a wavelength-converting material such as a phosphor or mixture of phosphors thereby exciting the phosphor material, which emits the secondary light. The peak wavelength of the secondary light depends on the type of phosphor material, which can be chosen to provide secondary light having a particular peak wavelength. This process is may be generally referred to as “wavelength conversion” and an LED combined with a wavelength-converting material, such as phosphor, to produce secondary light, may be described as a “wavelength-converted LED.” The term “LED source” as used herein refers to both a wavelength-converted LED and an LED that emits light at an associated peak wavelength/color.
Known decorative light sources may incorporate multiple LED sources emitting differently colored light outputs. By selection and positioning of the LEDs a decorative light source providing a multi-color light output may be produced. Such decorative light sources have been used in areas where general illumination from the light source is not required.
For general illumination, it is known to provide a separate LED light source providing a “white” light output. Such light sources may incorporate multiple LED sources emitting light of different colors that combine to produce light that appears white to an observer. It is often desirable to produce white light having a relatively high color rendering index (CRI). The color rendering index of a light source is an objective measure of the ability of the light generated by the source to accurately illuminate a broad range of colors. The color rendering index ranges from essentially zero for monochromatic sources to 100 for incandescent sources.
In addition, the chromaticity of a particular light source may be referred to as the “color point” of the source. For a white light source, the chromaticity may be referred to as the “white point” of the source. The white point of a white light source may fall along a locus of chromaticity points corresponding to the color of light emitted by a black-body radiator heated to a given temperature expressed in Kelvin (K). Accordingly, a white point may be identified by a correlated color temperature (CCT) of the light source, which is the temperature at which the heated black-body radiator matches the color or hue of the white light source. White light typically has a CCT of between about 2600 and 8000 K. White light with a CCT of 4000 has a yellowish color. White light with a CCT of 8000 K is more bluish in color, and may be referred to as “cool white.” “Warm white” may be used to describe white light with a CCT of between about 2600 K and 4000 K, which is more reddish in color.